Miniature coils on core with printed circuit

ABSTRACT

A method for producing a coil assembly includes overlaying printed circuit traces on a core. The traces include terminals for coupling to conductive connections on a base on which the coil assembly is to be mounted. Two or more wires are wrapped around the core so as to define two or more coils, wrapped in different, respective directions. The ends of the wires are coupled to the printed circuit traces, so as to connect the wires through the traces to the terminals.

FIELD OF THE INVENTION

The present invention relates generally to magnetic field transducers,and specifically to methods for producing miniature, multi-axis coilsand devices produced by such methods.

BACKGROUND OF THE INVENTION

Wireless devices commonly include magnetic field transducers in the formof one or more coils wound on a core. Such transducers may be used tosense or extract energy from external magnetic fields, using the currentor voltage that is induced in the coils by the fields. Transducers ofthis sort may alternatively be used as magnetic field generators, byapplying a driving current to the coils. One application of suchtransducers is in wireless position transponders, as described, forexample, by Govari in U.S. Patent Application Publication US2003/0120150 A1, and by Doron et al. in U.S. Pat. No. 6,239,724. Thedisclosures of both of these publications are incorporated herein byreference.

In some applications, multiple coils may be wound in differentdirections around the same core, in order to transmit or receivemagnetic fields along multiple different axes. For example, PCT patentpublication WO 00/38571 A1 and U.S. Pat. No. 6,261,247, to Ishikawa etal., whose disclosures are incorporated herein by reference, describe ananatomical position sensing system using one or more substantiallyspherical transponders for measuring relative positions and distances.The transponders are capable of receiving and transmitting RF signals,thus communicating between themselves and with a separate CPU. In oneembodiment, the transponder is fabricated on a spherical substrate andincludes nine coils in three sets of three coils. Each set is orthogonalto the others and comprises three coils: one transmit coil, one receivecoil, and one power coupling coil. The coil sets are grouped in thisfashion to ensure that at least one coil set is oriented to providepotentially optimum power coupling and signal communication therewith.

Another example of the use of multi-axis magnetic coils in a medicaldevice is described by Casper et al. in U.S. Pat. No. 5,167,626, whosedisclosure is also incorporated herein by reference. This patent relatesto a medical capsule device actuated by radio-frequency (RF) signal. Inone embodiment, three copper wire coils are orthogonally wound around acommon ferrite core. The core serves to increase the effectivecross-sectional area of the coils. The coil assembly thus provides forthe interception of more flux from a magnetic field transmitter andminimizes the dependence of received radio-frequency signal energy onthe orientation of the capsule device within the gastrointestinal tract.

There are techniques known in the art for forming or mounting asingle-axis magnetic coil on a circuit substrate. For example, U.S. Pat.No. 6,690,255, to Caramela et al., describes a surface-mountablecomponent comprising an elongated core having first and second ends andfirst and second supports for supporting the core. Each of the supportsdefines a receptacle for receiving one of the first and second ends ofthe core. Metallized pads are provided on the supports for electricallyconnecting and mounting the support to a printed circuit board. At leastone wire is wound about a portion of the core and has its endselectrically connected to the metallized pads of the supports.Components of this sort are available from Coilcraft Inc. (Cary, Ill.).

SUMMARY OF THE INVENTION

Embodiments of the present invention provide methods for producingmulti-axis coil assemblies that are suited for mounting on a base withconductive connections, such as a printed circuit substrate or a cableconnector. Although these methods may be used in producing coils of anysize, they are particularly advantageous in manufacturing miniaturetransponder and power coils that are to be integrated with other circuitelements. Such coils may be used, inter alia, in medical positionsensing applications.

In the embodiments described hereinbelow, printed circuit traces areoverlaid on a core, which may comprise magnetic or non-magneticmaterial. The traces comprise terminals for coupling to a base to whichthe coil assembly is to be mounted. In some embodiments, the traces areprinted directly onto the surface of a suitable core material, such as aceramic or plastic material. In other embodiments, the traces areprinted on a flexible printed circuit material, which is then wrappedaround the core. At least two coil wires are wrapped around the core indifferent, respective directions. The ends of the wires are connected tothe printed circuit traces overlying the core, which thus electricallycouple the wires through the traces to the terminals.

The coil assembly thus produced can be mounted on the base using thesame assembly techniques, such as surface-mount soldering or wirebonding, as are used for conventional circuit components. The novelproduction techniques provided by the present invention enhance themanufacturability and reliability of miniature coil assemblies, as wellas the convenience of integrating such coils with other circuitelements.

There is therefore provided, in accordance with an embodiment of thepresent invention, a method for producing a coil assembly, including:

overlaying printed circuit traces on a core, the traces includingterminals for coupling to conductive connections on a base on which thecoil assembly is to be mounted;

wrapping two or more wires around the core so as to define two or morecoils, wrapped in different, respective directions, the wires havingrespective ends; and

coupling the ends of the wires to the printed circuit traces, so as toconnect the wires through the traces to the terminals.

In some embodiments, the method includes mounting the coil assembly onthe base, and soldering or wire-bonding the terminals to the conductiveconnections so as to connect the wires to other circuitry via the base.

In a disclosed embodiment, overlaying the printed circuit tracesincludes printing the traces onto the core. Typically, the core includesa dielectric material, which is configured as a bobbin to receive thetwo or more wires, the bobbin including a flange upon which theterminals are printed. The dielectric material may include at least oneof a ceramic and a plastic material. Additionally or alternatively, thecore includes a magnetic material.

In another embodiment, overlaying the printed circuit traces includesprinting the traces on a flexible dielectric substrate, and placing thedielectric substrate over the core before wrapping the two or morewires.

In some embodiments, overlaying the printed circuit traces includesforming printed calibration coils over the core, and the method includesusing the printed calibration coils to calibrate a response of the coilsdefined by wrapping the two or more wires around the core to a magneticfield.

In disclosed embodiments, wrapping the two or more wires includeswrapping three coils around the core in respective, mutually-orthogonaldirections.

The base may include an area of a printed circuit substrate or may be apart of a cable connector.

There is also provided, in accordance with an embodiment of the presentinvention, a coil assembly, including:

a core;

printed circuit traces overlaid on the core, the traces includingterminals for coupling to conductive connections on a base on which thecoil assembly is to be mounted; and

two or more wires wrapped around the core in different, respectivedirections so as to define two or more coils, the wires havingrespective ends, which are coupled to the printed circuit traces, so asto connect the wires through the traces to the terminals.

There is additionally provided, in accordance with an embodiment of thepresent invention, a sensor, including:

a circuit substrate;

a coil assembly, which is mounted on the circuit substrate, and whichincludes:

-   -   a core;    -   printed circuit traces overlaid on the core, the traces        including terminals, which are coupled to the circuit substrate;        and    -   two or more wires wrapped around the core in different,        respective directions so as to define two or more coils, the        wires having respective ends, which are coupled to the printed        circuit traces, so as to connect the wires through the traces to        the terminals; and

a processing circuit, which is coupled to the circuit substrate so as toreceive signals produced by the coil assembly in response to a magneticfield, and which is adapted to process the signals so as to generatedata with respect to the magnetic field.

In a disclosed embodiment, the data generated by the processing circuitare indicative of a position of the sensor. The circuit substrate, coilassembly and processing circuit may be contained in a housing suitablefor insertion into a body of a patient.

There is further provided, in accordance with an embodiment of thepresent invention, a sensor, including:

a connector containing a base including conductive connections;

a coil assembly, which is mounted on the circuit substrate, and whichincludes:

-   -   a core;    -   printed circuit traces overlaid on the core, the traces        including terminals, which are coupled to the conductive        connections of the connector; and    -   two or more wires wrapped around the core in different,        respective directions so as to define two or more coils, the        wires having respective ends, which are coupled to the printed        circuit traces, so as to connect the wires through the traces to        the terminals;

a processing circuit, which is adapted to process signals produced bythe coil assembly in response to a magnetic field so as to generate datawith respect to the magnetic field; and

a cable, coupled between the conductive connections of the connector andthe processing circuit so as to convey the signals from the coilassembly to the processing circuit.

The present invention will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, pictorial illustration showing a magneticposition sensing system used in a medical application, in accordancewith an embodiment of the present invention;

FIG. 2 is a schematic, pictorial illustration showing a magneticposition transponder inside a bone implant, in accordance with anembodiment of the present invention;

FIG. 3A is a schematic, pictorial illustration showing a core on whichcircuit traces are printed, in accordance with an embodiment of thepresent invention;

FIG. 3B is a schematic, pictorial illustration showing a coil assemblywound on the core of FIG. 3A, in accordance with an embodiment of thepresent invention;

FIG. 4 is a schematic, frontal view of a flexible printed circuit, inaccordance with an embodiment of the present invention;

FIG. 5 is a schematic, pictorial illustration showing a coil assemblyusing the flexible printed circuit of FIG. 4, in accordance with anembodiment of the present invention; and

FIG. 6 is a schematic, pictorial illustration showing a coil and cableassembly, in accordance with another embodiment of the presentinvention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 is a schematic, pictorial illustration of a magnetic trackingsystem 20 used in surgery, in accordance with an embodiment of thepresent invention. A surgeon 22 performs a medical procedure on apatient 23 using a medical tool 24. Implants 26 are introduced into thepatient's body at a surgical site, which is located in this example in aleg 30 of the patient. The tracking system guides the surgeon inperforming the procedure, in this example a knee-joint operation, bymeasuring and presenting the positions of implants 26 and tool 24. Thesystem measures the location and orientation coordinates throughout aworking volume that comprises the surgical site.

The coordinates of tool 24 and implants 26 are determined relative tofield generators, such as location pads 34, which are fixed to thepatient's body. In the example shown in FIG. 1, the pads are placed onthe patient's calf and thigh, in proximity to implants 26. A signalgenerator unit 38 generates drive signals that drive the fieldgenerators, typically comprising field generating coils, in locationpads 34.

Implants 26 and tool 24 contain miniature, wireless sensor units, whichare described in detail hereinbelow. Each sensor unit comprises aposition sensor that is designed to sense the magnetic field in itsvicinity. The magnetic fields generated by location pads 34 inducecurrents in the position sensors of the sensor units fitted into tool 24and implants 26. In response to the induced currents (or correspondingvoltages), signal processing and transmitter circuits in each sensorunit generate and transmit position signals that are indicative of thelocation and orientation of the implant or tool. It is clear that inthis context, the position sensors must be very compact and functionwith high reliability.

The position signals are received by a wireless control unit 40, whichis coupled to a computer 41. The computer processes the received signalsin order to calculate the relative location and orientation coordinatesof tool 24 and implants 26. The results are typically presented to thesurgeon on a display 42.

Further details regarding position tracking systems of the sort shown inFIG. 1 can be found in U.S. patent application Ser. No. 11/063,094,filed Feb. 22, 2005, and in U.S. patent application Ser. No. 11/062,258,filed Feb. 18, 2005. These applications are assigned to the assignee ofthe present patent application, and their disclosures are incorporatedherein by reference. Alternatively, the principles of the presentinvention may be implemented in position tracking systems of othersorts, such as those noted in the Background of the Invention, as wellas in other applications of magnetic field transmission and reception,as are known in the art.

FIG. 2 is a schematic, pictorial illustration of a position sensor 50that is contained in implant 26, in accordance with an embodiment of thepresent invention. Alternatively, sensor 50 may be contained in orotherwise attached to other types of implants and invasive devices.Sensor 50 in this exemplary embodiment comprises a sensor coil assembly52, which comprises coil wires wound on a sensor core 54. The core maycomprise magnetic or non-magnetic material. Sensor 50 further comprisesa power coil assembly 62, and a wireless communication coil 60. Thecoils are mounted on a suitable substrate 56, such as a flexible printedcircuit board (PCB) and are coupled to electronic processing circuitry58, which is likewise mounted on the substrate. Circuitry 58 receivesand processes electrical signals generated by sensor coil assembly 52 inresponse to the magnetic field generated by location pad 34. Based onthese signals, circuitry 58 transmits position data to control unit 40.Further details of the construction and operation of circuitry 58 aredescribed in the above-mentioned U.S. Patent Application Publication US2003/0120150 A1 and in U.S. patent application Ser. No. 10/706,298,which is assigned to the assignee of the present patent application, andwhose disclosure is incorporated herein by reference.

Although for simplicity, FIG. 2 shows only a single coil in each ofsensor and power coil assemblies 52 and 62, in practice each assemblytypically comprises multiple coils, such as three sensor coils and threepower coils. (Multiple sensor coils wound on a common core are shown inFIGS. 3B and 5 below.) The sensor coils are wound together, inmutually-orthogonal directions, on core 54, while the power coils arewound together, in mutually-orthogonal directions, on another core 64.Alternatively, the sensor and power coils may be overlapped on the samecore, as described, for example in U.S. patent application Ser. No.10/754,751, filed Jan. 9, 2004, whose disclosure is incorporated hereinby reference.

FIG. 3A is a schematic, pictorial illustration of core 54, in accordancewith an embodiment of the present invention. Core 54 typically comprisesa dielectric material, such as a suitable ceramic or plastic material,such as polyetheretherketone (PEEK), which is manufactured in the formof a bobbin, with typical dimensions of about 2×2×5 mm. Optionally, amagnetic ceramic material may be used. Metal terminal pads 70 areprinted onto the sides and flanges 72 of the bobbin, using aphotolithographic process, for example. The terminal pads printed ontothe base of the core, at the outer side of flanges 72, allow the coreitself to be mounted and soldered onto a printed circuit board, such assubstrate 56, using surface mount manufacturing techniques. Printedcircuit traces 73 connect the terminal pads on the sides of the core tothe terminal pads on the outer surfaces of the bobbins.

FIG. 3B is a schematic, pictorial illustration showing sensor coilassembly 52, in accordance with an embodiment of the present invention.In this embodiment, three separate coils 74, 76, 78 of thin wire havebeen wound on core 54 (hidden in this figure). Each of the coils iswrapped around a different, orthogonal axis. The size of the wire andnumber of turns depends on application requirements, for example, moreturns of thinner wire for sensor coil assembly 52, fewer turns ofthicker wire for power coil assembly 62. In different implementations,the inventors have used wires of diameter between 10 and 70 μm, withbetween 40 and 3000 turns of wire around the core. Other implementationswill be apparent to those skilled in the art.

To produce assembly 52, core 54 is mounted so as to rotate about theaxis of coil 74, and a suitable wire is fastened to the core. The coreis then rotated about the axis, and the wire is fed out from a spooluntil the proper number of turns have been wound on the core. The coreis then shifted to rotate about the axis of coil 76, and the core isthen rotated so as to wind coil 76 over coil 74. Optionally, adielectric separator (not shown in the figures) is placed over coil 74before winding coil 76, in order to reduce parasitic coupling betweenthe two coils. Finally, coil 78 is wound over coil 76 in the samemanner. Wire ends 79 of each of the coils are then soldered toappropriate points on terminal pads 70, thus electrically coupling thecoil wires to pads on the bottom of flanges 72. Assembly 52 can now bemounted on a printed circuit substrate, such as substrate 56, in theorientation shown in FIG. 3B.

FIG. 4 is a schematic, frontal view of a flexible printed circuit 80, inaccordance with an embodiment of the present invention. The flexibleprinted circuit may be wrapped around a core, as shown below in FIG. 5,when it is not possible or desirable to print circuit traces directly onthe core, as in the preceding embodiment. Circuit 80 comprises a thin,flexible dielectric substrate material 82, such as Mylar®, on whichconductive traces 83 are printed. Two terminals 84 are also provided incircuit 80 for each of the X-, Y- and Z-coils that will be wrapped onthe core. Terminals 84 are coupled by traces 83 to contacts 86, whichprotrude at the edge of substrate 82.

FIG. 5 is a schematic, pictorial illustration of a coil assembly 90,based on printed circuit 80, in accordance with an embodiment of thepresent invention. To produce assembly 90, printed circuit 80 is wrappedaround a core 92, such as a ferrite, and fastened in place, using asuitable glue, for example. The six segments of the printed circuit aresized to match the faces of the core. Although core 92 is shown in FIG.5 to have a cubic shape, other core shapes may likewise be used, withappropriate adjustment to the shape and size of printed circuit 80. Eachof coils 74, 76 and 78 is then wound on core 92 in the manner describedabove with regard to coil assembly 52: end 79 of the coil wire isinserted into one of terminals 84, and the core is then rotated to wrapthe wire around the core in the proper direction. After completing thewinding, the other end of the coil wire is inserted into the otherterminal.

When flexible printed circuit 80 has been wrapped around core 92, andthe coils have been wound over the printed circuit, contacts 86 remainaccessible. These contacts may be soldered to a circuit substratedirectly or connected by bonding wires. Thus, coil assembly 60 can bemounted on a substrate, such as substrate 56, along with otherelectronic components of the sensor, using surface mounting techniquesif desired.

In magnetic sensing applications, deviations in the geometry of coils75, 76, 78 can cause variations in the responses of the coils to anapplied magnetic field and thus compromise the accuracy of the sensor.To address this problem, calibration coils 88 may optionally be printedas traces on flexible printed circuit 80, typically on the inner surface(i.e., on the side facing toward core 92, away from coils 74, 76, 78).These calibration coils are likewise connected by traces (not shown) tocontacts 86, and may thus be coupled to circuitry on substrate 56. Sincethese printed calibration coils have a precisely-known geometry, theycan be used to calibrate the response of the wire-wound coils, in orderto compensate for manufacturing variability in the wire-wound coils. Forexample, the response of the printed calibration coils to an externalmagnetic field can be used as a calibration benchmark for the wire-woundcoils or, alternatively, the response of the wire-wound coils to amagnetic field generated by driving the printed calibration coils can bemeasured for calibration purposes.

FIG. 6 is a schematic, pictorial illustration showing a coil assembly100, which is designed to mate with a connector 106, in accordance withanother embodiment of the present invention. Assembly 100 is similar indesign and method of manufacture to assembly 52 (FIG. 3B), and comprisesa core 102 with coils 104 wound thereon. The wire ends of the coils arethen soldered to appropriate points on terminal pads 70, as describedabove.

In the present embodiment, however, flanges 72 of coil assembly 100 aremounted on a base 112 in connector 106, which couples the coil assemblyto a multi-conductor cable 108. Base 112 may comprise conductivecontacts that engage the terminals on flanges 72. Additionally oralternatively, conductors 110 of cable 108 may extend out of connector106 and connect, typically by wire bonding or another suitabletechnique, to pads 70. When assembly 100 comprises three coils 104, forexample, all six ends of the coil wires may be connected easily andreliably to respective conductors of cable 108 using one or both ofthese techniques.

After connecting coil assembly 100 to connector 106, the coil assembly(and possibly the connector, as well) may be encapsulated in a sealed,biocompatible housing, and may then be inserted into the body of apatient, as described above. Cable 108 conveys the signals from the coilassembly to processing circuitry outside the body, which processes thesignals to determine position coordinates of the coil assembly asdescribed above. This arrangement, in which the coil alone is containedin the sensor unit that is inserted into the patient's body and isconnected to the processing circuitry by cable 108, is useful inminimizing the size of the sensor unit and avoiding problems that may beassociated with wireless power and data transmission to and from thesensor.

Although the embodiments described above relate particularly toconstruction of magnetic field sensors in a position trackingapplication, the novel techniques described above for overlayingconductive traces on a core and connecting coil wires to such traces maybe used, mutatis mutandis, in other applications and configurations. Forexample, multi-axis coil components may be made in this way for purposesof generating and transmitting magnetic fields. Furthermore, theconductive traces that are overlaid on the core of an inductive coil inaccordance with the techniques described above may also be used forintegrating circuitry of other types with the coil in a single,self-contained unit.

It will thus be appreciated that the embodiments described above arecited by way of example, and that the present invention is not limitedto what has been particularly shown and described hereinabove. Rather,the scope of the present invention includes both combinations andsubcombinations of the various features described hereinabove, as wellas variations and modifications thereof which would occur to personsskilled in the art upon reading the foregoing description and which arenot disclosed in the prior art.

1. A method for producing a coil assembly, comprising: overlayingprinted circuit traces on a core, the traces comprising terminals forcoupling to conductive connections on a base on which the coil assemblyis to be mounted; wrapping two or more wires around the core so as todefine two or more coils, wrapped in different, respective directions,the wires having respective ends; and coupling the ends of the wires tothe printed circuit traces, so as to connect the wires through thetraces to the terminals.
 2. The method according to claim 1, andcomprising mounting the coil assembly on the base, and soldering theterminals to the conductive connections so as to connect the wires toother circuitry via the base.
 3. The method according to claim 1, andcomprising mounting the coil assembly on the base, and wire-bonding theterminals to the conductive connections so as to connect the wires toother circuitry via the base.
 4. The method according to claim 1,wherein overlaying the printed circuit traces comprises printing thetraces onto the core.
 5. The method according to claim 4, wherein thecore comprises a dielectric material, which is configured as a bobbin toreceive the two or more wires, the bobbin comprising a flange upon whichthe terminals are printed.
 6. The method according to claim 5, whereinthe dielectric material comprises at least one of a ceramic and aplastic material.
 7. The method according to claim 1, wherein the corecomprises a magnetic material.
 8. The method according to claim 1,wherein overlaying the printed circuit traces comprises printing thetraces on a flexible dielectric substrate, and placing the dielectricsubstrate over the core before wrapping the two or more wires.
 9. Themethod according to claim 1, wherein overlaying the printed circuittraces comprises forming printed calibration coils over the core, andcomprising using the printed calibration coils to calibrate a responseof the coils defined by wrapping the two or more wires around the coreto a magnetic field.
 10. The method according to claim 1, whereinwrapping the two or more wires comprises wrapping three coils around thecore in respective, mutually-orthogonal directions.
 11. The methodaccording to claim 1, wherein the base comprises an area of a printedcircuit substrate.
 12. The method according to claim 1, wherein the baseis a part of a cable connector.
 13. A coil assembly, comprising: a core;printed circuit traces overlaid on the core, the traces comprisingterminals for coupling to conductive connections on a base on which thecoil assembly is to be mounted; and two or more wires wrapped around thecore in different, respective directions so as to define two or morecoils, the wires having respective ends, which are coupled to theprinted circuit traces, so as to connect the wires through the traces tothe terminals.
 14. The assembly according to claim 13, wherein thetraces are printed onto the core.
 15. The assembly according to claim14, wherein the core comprises a dielectric material, which isconfigured as a bobbin to receive the two or more wires, the bobbincomprising a flange upon which the terminals are printed.
 16. Theassembly according to claim 15, wherein the dielectric materialcomprises at least one of a ceramic and a plastic material.
 17. Theassembly according to claim 13, wherein the core comprises a magneticmaterial.
 18. The assembly according to claim 13, and comprising aflexible dielectric substrate, upon which the circuit traces areprinted, wherein the dielectric substrate is placed over the core beforewrapping the two or more wires.
 19. The assembly according to claim 13,wherein the printed circuit traces comprise printed calibration coils,which are used to calibrate a response of the coils defined by wrappingthe two or more wires around the core to a magnetic field.
 20. Theassembly according to claim 13, wherein the two or more wires arewrapped around the core so as to define three coils, which are wrappedin respective, mutually-orthogonal directions.
 21. The assemblyaccording to claim 13, wherein the base comprises an area of a printedcircuit substrate.
 22. The method according to claim 13, wherein thebase is a part of a cable connector.
 23. A sensor, comprising: a circuitsubstrate; a coil assembly, which is mounted on the circuit substrate,and which comprises: a core; printed circuit traces overlaid on thecore, the traces comprising terminals, which are coupled to the circuitsubstrate; and two or more wires wrapped around the core in different,respective directions so as to define two or more coils, the wireshaving respective ends, which are coupled to the printed circuit traces,so as to connect the wires through the traces to the terminals; and aprocessing circuit, which is coupled to the circuit substrate so as toreceive signals produced by the coil assembly in response to a magneticfield, and which is adapted to process the signals so as to generatedata with respect to the magnetic field.
 24. The sensor according toclaim 23, wherein the data generated by the processing circuit areindicative of a position of the sensor.
 25. The sensor according toclaim 24, wherein the circuit substrate, coil assembly and processingcircuit are contained in a housing suitable for insertion into a body ofa patient.
 26. A sensor, comprising: a connector containing a basecomprising conductive connections; a coil assembly, which is mounted onthe circuit substrate, and which comprises: a core; printed circuittraces overlaid on the core, the traces comprising terminals, which arecoupled to the conductive connections of the connector; and two or morewires wrapped around the core in different, respective directions so asto define two or more coils, the wires having respective ends, which arecoupled to the printed circuit traces, so as to connect the wiresthrough the traces to the terminals; a processing circuit, which isadapted to process signals produced by the coil assembly in response toa magnetic field so as to generate data with respect to the magneticfield; and a cable, coupled between the conductive connections of theconnector and the processing circuit so as to convey the signals fromthe coil assembly to the processing circuit.
 27. The sensor according toclaim 26, wherein the data generated by the processing circuit areindicative of a position of the sensor.
 28. The sensor according toclaim 26, wherein the coil assembly is encapsulated in a housingsuitable for insertion into a body of a patient.